MPN #N250    


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All-tube monoblock amplifier with balanced and unbalanced inputs

The Manley 500 and 250 Watt Monoblocks are our most powerful push-pull production-models. Both the circuit design and the selected componentry have been refined over years and years of development. Reliability that you can depend upon combined with musical accuracy and emotional authority is what these amplifiers promise- and deliver. They are able to switch operation modes allowing the listener to choose between the sonically seductive qualities of triode and the more powerful Ultra-Linear configuration. We use big, beefy reservoir capacitors in the high voltage supplies giving plenty of instant energy for dynamic performance of transient peaks and bass impact and weight which often exceeds that of rival solid-state amplifiers. We run high voltages on the plates of the output tubes but operate them at lower current which will result in their longer life. Although each output tube has its own bias-adjust, We carefully fit each amplifier with computer-batched tubes for optimum performance. The bias adjustment pots and measuring points are conveniently located behind the oval front panel insert.

To avoid a heavy power drain when the cold amplifier is first switched on, we conceived a "Soft-Start" mode which also functions as an "Ever-Warm" position allowing the amplifiers to be always warmed up for pleasurable listening. Each amplifier only consumes 30 watts of power in Ever-Warm mode. A blinking green LED reminds the user that the amplifier is in warm-up mode because as all the power supplies are at half-voltage, the amplifier will still operate at half power when the Ever-Warm mode is engaged, so the user should use the MUTE switch when in this mode.

The front-panel mute switch and angled-back chassis make it easier to hook up the interconnects, speaker cables, and IEC power cord.

In our own in-house magnetics department, our R&D team completely redesigned all of our output transformers in 1998 with the goal to reclaim that luscious rich mid-range of our vintage designs. In 2013 we reworked the output transformer to operate the output stage in Ultra-Linear mode which is a great sounding balance between the detail of triode and the brawn of Tetrode. We also specifically set out to achieve a deeper bottom register at higher power with lower distortion. Hours and hours of listening tests, measurements, and fine-tuning brought an exciting and stunning result to our ears. We hope you will agree.
  • ALL-TUBE monoblock design: uses 10 x Tungsol EL34B output tubes
  • Driver Stage: High current double 12BH7EH (x2)
  • Input Tube: 12AT7
  • BALANCED & UNBALANCED inputs: RCA and XLR jacks (switchable)
  • MANLEY IRON Input Transformer for the XLR: 2:1 ratio designed and wound at Manley Labs
  • MUTE switch: on front panel
  • TRIODE / Ultra-Linear output mode switching: on front panel
  • SOFT-START turn on mode: minimizes in-rush current by first powering up amplifier to half voltages
  • EVER-WARM mode: for standby keeps tubes warmed up at half voltages
  • MANLEY IRON Output Transformer: designed and wound at Manley Labs
  • Front panel bias measurement and adjust: Concealed under the black oval insert
  • Output Tube Standing Current: 30mA
  • Set Bias for: 300mVDC measured across each bias tip jack to ground
  • Large filter / reservoir capacitors: 3800uF x 2
  • Angled rear of chassis: provides for easy connections
  • WBT binding posts: CE compliant for European models
  • Input Sensitivity RCA: Triode = 1.17 V; UL = 1.38 V for full power into 5 Ohms
  • Input Sensitivity XLR: Triode = 2.56 V; Tetrode = 3.05 V for full power into 5 Ohms
  • Input Sensitivity RCA Triode: 98.3 mV; UL = 86.6 mV for 1 Watt into 5 Ohms
  • Input Sensitivity XLR Triode: 227 mV; UL = 200 mV for 1 Watt into 5 Ohms
  • Gain RCA: Triode = 27.2 dB; UL = 28.3 dB
  • Gain XLR: Triode = 21.2 dB; UL = 22.3 dB
  • Input Impedance RCA: 130 kOhm @ 1KHz
  • Input Impedance XLR: 278 kOhm @ 1KHz; 20 kOhms @ 20KHz; 28 kOhm @ 20Hz
  • Actual Output Impedance Triode: 0.610 Ohm
  • Actual Output Impedance Tetrode: 0.698 Ohm
  • Optimum Speaker Load: 5 Ohms
  • Damping Factor Triode: 13.1
  • Damping Factor Tetrode: 11.5
  • S/N Ratio: 94 dB A-WGT at 1 Watt into 5 Ohms
  • Dynamic Range: 114 dB A-WGT
  • Noise Floor: -84 dB or 50 ┬ÁV A-WGT 1 Watt into 5 Ohms w/Shorted Input
  • Frequency response -1 dB: Triode = 10 Hz - 30 kHz
  • Full Power frequency response -1 dB: Triode = 10 Hz - 33 kHz; UL = 10 Hz - 20 kHz to reach 1.5% THD into 5 Ohms
  • Distortion: Triode = 0.052%; UL = 0.37% BW 10 Hz - 500 kHz at 1 Watt into 5 Ohms
  • Full Power Triode: 140 W @ 1.5% THD into 5 Ohms
  • Full Power UL: 250 W @ 1.5% THD into 5 Ohms
  • Power Consumption: 40 Watts in "EVER-WARM" mode
  • Power Consumption Idle: 335 Watts
  • Maximum Power Consumption: 710 Watts at full power
  • Operating Mains Voltage: Factory set for 100V, 120V or 220-240VAC operation for original destination country's mains voltage.
  • Operating Mains Voltage: changeable with power transformer replacement and fuse value change.
  • Mains Voltage Frequency: 50 Hz or 60 Hz
  • Mains Fuse 100-120VAC operation: MDA 10 Amp SLO-BLO Ceramic Time-Delay fuse
  • Mains Fuse 220-240VAC operation: MDA 8 Amp SLO-BLO Ceramic Time-Delay fuse
  • B+ Fuse: MDA 1 1/2A SLO-BLO Ceramic Time-Delay fuse
  • Badge Illumination: Units produced before 4/2003 use 8V, 0.3A "Fuse-Lamp" 1/4" X 1 1/4"
  • - Serial numbers after N250188 use LED illumination which probably won't burn out
  • Power Cord: Detachable IEC standard. Appropriate power cord supplied for destination country
  • Unit Dimensions: W=19" x D=13" x H=9" each
  • Unit Weight: 69 lbs. each
  • Shipping Box Dimensions: 22" x 19" x 18"
  • Shipping Weight: 79 lbs. each
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